System and method for frequency management in a communications positioning device

ABSTRACT

A frequency management scheme for a hybrid communications/positioning device, such as a cellular/GPS or other combined device, generates a local clock signal for the communications portion of the device, using a crystal oscillator or other part. The oscillator output may be corrected by way of an automatic frequency control (AFC) circuit or software, to drive the frequency of that clock signal to a high accuracy. The base oscillator may be delivered to a phase locked loop to drive a high-frequency clock for the cellular or other communications portion of the hybrid device, which clock signal may also be frequency-converted to drive a GPS or other positioning receiver. The extraction of a base GPS clock from the radio frequency reference eliminates the need for a second oscillator or synthesizer for that portion of the hybrid device. In embodiments, AFC tuning on the cellular clock may be omitted and the high frequency clock signal divided down for delivery to the GPS or other positioning receiver may be adjusted via a frequency prescaler, or other module.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application relates to and claims priority from U.S.Provisional Application Serial No. 60/380,832 filed May 17, 2002, whichapplication is incorporated by reference. This application is alsorelated to the subject matter of U.S. application Ser. No. ______entitled “SYSTEM AND METHOD FOR FREQUENCY MANAGEMENT IN A COMMUNICATIONSPOSITIONING DEVICE”, having a docket No. CM03713J and filed of even datewith this application, having the same inventors as this application,being assigned to or under obligation of assignment to the same entityas this application, and which application is incorporated by referencein this application.

FIELD OF THE INVENTION

[0002] The invention relates to the field of communications, and moreparticularly to techniques for generating and managing precisionfrequency sources in cellular telephones or other communications deviceshaving a positioning capability, such as Global Positioning System (GPS)or other location service.

BACKGROUND OF THE INVENTION

[0003] GPS receivers can be characterized by performance criteria suchas acquisition and tracking time, which reflect the amount of processingnecessary to detect and lock on to GPS satellite signals and hence theamount of time needed to begin accurately reporting a user's position.The acquisition, tracking, sensitivity and other performance parametersof GPS receivers can be affected by a variety of factors. Those factorsinclude the precision with which frequency references for radiofrequency detection and other purposes can be generated and managedwithin the device. L1 GPS signals used for civilian coarse acquisition(C/A) purposes are broadcast at 1.575 GHz from the associated NAVSTARsatellites. Russian GLONASS satellites broadcast in a similar frequencyrange.

[0004] Handheld, vehicle-mounted, stationary and other GPS and otherpositioning receivers require frequency stability in their clocksgenerally in the range of a few parts per million or less to accuratelyderive Doppler and other data from those signals, and thereforetriangulate a precise receiver position within a reasonable acquisitiontime.

[0005] Recently, market trends have developed toward GPS functionalitycombined with other communications services. Various wireless devices,such as cellular telephones, digital pagers, wireless personal digitalassistants, 802.11a and other clients may all be combined with GPSlocation receivers for various applications.

[0006] However, the accuracy of reference clocks generally employed incellular telephones and other communications devices may generally notbe as great as that needed for useful GPS service, which as noted mayrequire extended accuracy to within at least a few parts per million,down to tenths of 1 part per million or less for increased trackingperformance. Cellular telephones on the other hand may containuncompensated oscillators accurate to within only perhaps five to tensof parts per million, depending on implementation. Cellular devices maytolerate higher frequency variability in part because handsets or otherdevices may be able to derive a stable frequency reference from a basestation or the wireless network, itself.

[0007] In the case of a GPS receiver combined with a cellular telephonefor caller location service as mandated by the Federal CommunicationsCommission, a cellular telephone's local crystal oscillator, tuned to16.8 MHz or another base frequency, may for instance have a frequencyvariance of ±30 ppm or more or less. A cellular handset's internal clockmay therefore not be sufficient to drive GPS circuitry in a combineddevice for useful GPS operation by itself. Temperature compensationcircuits operating on ordinary crystal oscillators may improve thefrequency reference to perhaps ±5 ppm or so, although those types ofparts may add to the cost of a relatively low-cost mobile device.Solutions such as supplying two corrected reference oscillators, one forGPS and one for cellular or other communications service at differentfrequencies, for instance, would not be likely to be economical in acombined device. Other problems exist.

SUMMARY OF THE INVENTION

[0008] The invention overcoming these and other problems in the artrelates in one regard to a system and method for frequency management ina combined communications/positioning system, in which a stable basereference may be extracted for GPS purposes from a high-frequencyreference used to drive the demodulation of signals on thecommunications side of the device. The invention in one regard thusallows both cellular and GPS circuits to be controlled from one source,without a need for a second oscillator in the GPS receiver portion ofthe device. According to the invention in one regard, the GPS circuitrymay be driven by a signal from a phase locked loop generating a radiolocal oscillator for demodulation, downconversion or othercommunications operations, divided down to an appropriate base GPSfrequency. The base oscillator driving the communications portion of thecombined device may be corrected using for instance software temperaturecorrection, hardware temperature correction, measurement of frequencybias at time of manufacture, automatic frequency control (AFC) or othertechniques to establish accuracy in the communications portion of thedevice to ±5 ppm or more or less. The GPS receiver component mayconsequently be driven with corresponding accuracy and therefore neednot have a local oscillator of its own, while still achieving sufficientGPS performance at comparatively low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The invention will be described with reference to theaccompanying drawings, in which like elements are referenced with likenumbers, and in which:

[0010]FIG. 1 illustrates a frequency management architecture, accordingto an embodiment of the invention.

[0011]FIG. 2 illustrates a flowchart of frequency management processing,according to an embodiment of the invention.

[0012]FIG. 3 illustrates a frequency management architecture, accordingto an embodiment of the invention.

[0013]FIG. 4 illustrates a frequency management architecture, accordingto an embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0014] An architecture in which a frequency management system accordingto the invention may be implemented is illustrated in FIG. 1, in which acombined communications/positioning device incorporates both GPSreceiver 124 and a communications transceiver 120. The communicationstransceiver 120 of the combined device may be or include for instance aportable radio, cellular telephone, two-way or other pager, wirelessmodem, wireless personal digital assistant or other device that receivesor transmits a radio, optical or other wireless communications signal.

[0015] The combined communications/positioning device as illustrated maycontain a base oscillator 102 to provide a frequency reference toultimately drive the communications transceiver 120. In embodiments baseoscillator 102 may be a free-running, uncompensated reference part. Thebase frequency of the base oscillator 102 may be set to valuescompatible with cellular or other operation at 800/900 MHz, 1900 MHz orother frequency ranges. The base oscillator 102 may for example be setto 16.8 MHz or other frequencies which may be multiplied to carrierranges. An uncompensated crystal oscillator such as may be used toimplement base oscillator 102 may by itself typically exhibit, forinstance, a frequency deviation of ±30 ppm or more or less.

[0016] In embodiments the output of base oscillator 102 may be processedor corrected using hardware, software or other techniques to improvefrequency stability. Techniques to control base oscillator 102 mayinclude, for instance, the use of factory measurement data 104 tocompensate for detected frequency bias or offset in the manufacturedpart, and other artifacts. Factory measurement data 104 may in oneregard be stored in the combined device and used to re-center thefrequency of base oscillator 102 during operation, via software orotherwise. Other adjustments are possible.

[0017] In embodiments, base oscillator 102 may likewise be controlledfor frequency drift or other artifacts associated with varyingtemperature, using temperature frequency control module 106. Temperaturefrequency control module 106 may in embodiments be implemented usinghardware, software, firmware, or combinations of the same to correctbase oscillator 102.

[0018] Temperature frequency control module 106 may, for instance, inembodiments be combined in the base oscillator 102 using hardwarecomponents such as a temperature-controlled crystal oscillator (TCXO) orother hardware-corrected oscillator or reference part. A hardware TXCOmay for instance exhibit a frequency accuracy of ±5 ppm or more or less,depending on manufacturing, design or other factors.

[0019] In embodiments, temperature frequency control module 106 may beimplemented using software control such as a temperature frequencycontrol (TFC) or other algorithm, to sense and adjust frequency settingsbased for instance on temperature, power and other parameters.

[0020] The output of the base oscillator 102 may in embodiments beprocessed to further increase the accuracy of the frequency reference.As illustrated in FIG. 1, the frequency tracking control module 108 mayapply correction to the base oscillator 102 to increase the accuracy ofthe frequency output. In embodiments, the frequency tracking controlmodule 108 may be implemented in hardware, software, firmware orcombinations of the same.

[0021] In embodiments, the frequency tracking control module 108 may beimplemented in hardware, such as an automatic frequency control (AFC)circuit, of the superheterodyne, direct conversion or other type lockingto a cellular or other carrier.

[0022] In embodiments, the frequency tracking control module 108 may beimplemented in software algorithms, with correction instead for instanceapplied to a synthesizer or other associated part by programming logicor otherwise to achieve enhanced frequency precision.

[0023] In cellular or other communications networks, the accuracy of thefrequency reference corrected by frequency tracking control module 108may for instance reach ±0.2 ppm or more or less, in part becausecellular or other base stations may maintain accurate cesium or otherclock references which may be broadcast over their communicationschannels. Frequency tracking control module 108 as illustrated may forinstance communicate with and receive input from communicationstransceiver 120 to perform frequency tracking, by negative feedback orother techniques.

[0024] The frequency tracking control module 108 as illustrated may beapplied to a phase locked loop 110 to drive operating frequencies forcellular or other communications or other operations. The phase lockedloop 110 may include a phase comparator 112, to compare the phase of thebase oscillator 102 with the phase of a high-frequency oscillator 116.High-frequency oscillator 116 may for instance be implemented as avoltage controlled high-frequency oscillator (VCO) generatingfrequencies, for instance, in the 800/900 MHz, 1900 MHz or other rangesfor cellular or other operation. A loop filter 114 may low-pass filterthe output of the phase comparator 112 to remove higher frequencyartifacts or other noise.

[0025] The output of the loop filter 114 may in turn drive thehigh-frequency oscillator 116 to operating frequencies, which throughthe return provided by loop divider 118 completes a closed feedback loopto phase comparator 112. The phase of the high-frequency oscillator 116is thereby locked to the phase of the base oscillator 102, so that thephase angle between them remains zero or approximately zero, or at afixed or approximately fixed separation during operation.

[0026] The clock reference of the high-frequency oscillator 116 forms anoutput of the phase locked loop 110, which may in turn drivecommunications transceiver 120 to demodulate, downconvert and receivethe wireless signals broadcast to the communications device, or performother communications operations. In the embodiment illustrated in FIG.1, each of the factory measurement data 104, temperature frequencycontrol module 106 and frequency tracking control module 108 maylikewise be in communication with loop divider 118 of phase locked loop110, to correlate the adjustment of the output of phase locked loop 110used to drive communications transceiver 120. For instance, inembodiments comparatively fine or other adjustments may be made to theratio of loop divider 118, according to inputs from those correctivedata or modules.

[0027] According to embodiments of the invention, the output of thephase locked loop 110 may also be used to drive GPS receiver 124 withinthe combined device. The GPS receiver 124 may consequently acquire andtrack GPS signals without the added costs of incorporating an additionallocal oscillator as well as associated automatic frequency control (AFC)or other signal processing circuitry or software to enhance thefrequency reference for that portion of the combined device.

[0028] According to the embodiment illustrated in FIG. 1, a frequencyreference output from phase locked loop 110 may be communicated to theGPS receiver 124 from the communications or other circuitry, withoutrequiring a local oscillator apparatus in the GPS receiver 124. In thisembodiment, the frequency reference derived from base oscillator 102 mayfor instance be divided by GPS divider 122 to a desired GPS frequency.GPS divider 122 as illustrated may likewise communicate with and receiveinput from the frequency tracking control module 108, to refine dividerratios or other adjust processing parameters. The output of GPS divider122 may be communicated via filter 128 to remove noise, isolatedemodulation frequencies or perform other signal conditioning. Inembodiments the frequency division may for instance be performed usingGPS divider 122 as a separate part, by an auxiliary synthesizerprescaler contained as part of a synthesizer or other part, or by otherparts or software.

[0029] Since the accuracy of the output of the GPS divider 122 may trackthe accuracy of the base oscillator 102 treated by temperature, AFC,phase locked loop or other correction, this downconversion process mayprovide a reference signal to the GPS receiver 124 having an accuracy inembodiments of ±5 ppm to 0.2 ppm or more or less. This may eliminate anynecessity to introduce a separate oscillator or a step-up phase lockedloop in the GPS receiver 124 itself, reducing cost and increasingreliability in the resulting device.

[0030] Processing according to the invention in one regard isillustrated in FIG. 2. In step 202, processing begins. In step 204, baseoscillator 102 may generate a 16.8 MHz or other clock reference signal,for communications or other purposes. In step 206, offset correction, ifused, may be applied to center or otherwise correct the output of baseoscillator 102, based on factory measurement data 104 or other data. Instep 208, temperature correction using temperature frequency controlmodule 106, if used, may be applied to correct the output of baseoscillator 102 to increase frequency accuracy or stability, for instanceusing software, circuitry, or other techniques.

[0031] In step 210, the output of the base oscillator 102 may betransmitted to the phase locked loop 110. In step 212, the phase lockedloop 110 may lock the phase of high-frequency oscillator 116 to thephase of base oscillator 102. In step 214, the output of phase lockedloop 110 may drive communications transceiver 120, for instance forcellular or other operation.

[0032] In step 216, the communications transceiver 120 may register orcommunicate with a cellular base station or other remote or othertransceiver. In step 218, an AFC or other frequency tracking control maybe performed on base oscillator 102, for instance by software, circuitryor other techniques.

[0033] In step 220, the output of phase locked loop 110 may becommunicated to GPS divider 122, for instance to divide the incomingreference signal down to base frequencies which may be used to drive GPSoperation, such as, for example, 24.5535 MHz or other frequencies.

[0034] In step 222, GPS divider 122 may generate an output referencesignal according to the divide ratio, which in embodiments may beprogrammable or dynamically adjusted according to communications orother conditions. In other embodiments, the divide ratio may behardwired, or be flashed or otherwise be set to remain relativelystatic.

[0035] In step 224, the output of GPS divider 122 may drive GPS receiver124 for instance via filter 128 for radio frequency demodulation orother operations. In step 226, processing may end, repeat, or return toa prior processing point.

[0036] In an embodiment of the invention illustrated in FIG. 3, theoutput of base oscillator 102 may be communicated to the phase lockedloop 110 omitting any frequency tracking control module, if thatcorrection is not needed to achieve satisfactory accuracy in givenimplementations. In such embodiments, the divide ratio of the GPSdivider 122 may in cases be dynamically or otherwise adjusted, forinstance in fine increments, to tune the resulting GPS frequencyreference delivered to GPS receiver 124 without the benefit of an AFC orother circuit or algorithm. In this case, other compensation, such asthat performed or effected by factory measurement data 104 andtemperature frequency control module 106, may still be performed on baseoscillator 102 as well as communicated to loop divider 118 or otherparts of phase locked loop 110. Other types of correction orcompensation to base oscillator 102, such as correction using factorymeasurement data 104 or other data, may also be applied, alone or inconjunction with temperature control or other techniques.

[0037] As noted, in this embodiment the divide ratio of the GPS divider122 may for instance be adjusted to alter the clock reference deliveredto the GPS receiver 124 by comparatively fine, or in implementationsmore or less coarse, amounts. The divide ratio may illustratively be aninteger N, but floating point and other divide ratios are possible. Theomission of frequency tracking correction or other types of compensationon base oscillator 102 in embodiments may depend, in part, on factorssuch as the frequency range of the communications transceiver 120, thedetected offset of the base oscillator 102 during manufacture, thenumerical precision of the divide ratio effected by GPS divider 122, orother factors.

[0038] In an embodiment illustrated in FIG. 4, the phase locked loop 110may drive a synthesizer 126 or other part to generate other desiredfrequencies for cellular or other operation, rather than drive thecommunications transceiver 120 directly. According to this embodiment,the frequency reference may be programmed or scaled according to designneeds, such as for instance for multi-band operation for cellularhandsets, or other implementations. Likewise, in embodiments the GPSdivider 122 may in turn drive a synthesizer or other part to generatedesired frequency ranges, rather than drive GPS receiver 124 directly.Other combinations are possible.

[0039] The foregoing description of the invention is illustrative, andvariations in configuration and implementation will occur to personsskilled in the art. For instance, while the phase locked loop 110locking high-frequency oscillator 116 to base oscillator 102 has beengenerally described in terms of a negative feedback topology including acomparator, loop filter, high-frequency oscillator and feedback divider,in embodiments the phase locking function may be implemented in othercircuit configurations, by software algorithms, or other combinations ofhardware and software.

[0040] Further, while the communications transceiver 120 and relatedcircuitry has generally been described in terms of a cellular telephoneequipped with positioning capability, other communications receivers ortransceivers may be used. For instance, in embodiments a passivecommunications receiver rather than a two-way communications transceiver120 may be implemented. Other receivers, transceivers, modems or othercommunications components may be used. For instance, in embodimentssatellite-based communications receivers or transceivers, data links orother wired, wireless, optical and other interfaces or channels may beused. Likewise again, while the invention has generally been describedin terms of a GPS device as the positioning receiver, other positioningsystems or a combination of positioning systems may be used.Furthermore, while the invention has generally been described in termsof a pair of communications and positioning receivers, modems orelements, in embodiments three or more communications, positioning orother receivers, modems or other communications devices may be employed.The invention is accordingly intended to be limited only by thefollowing claims.

We claim:
 1. A system for generating a frequency reference in a hybridcommunications device, comprising: a clock source in a communicationsportion of the hybrid communications device, the clock source generatinga clock signal at a first frequency; a frequency correction module,communicating with the clock source, the frequency correction modulegenerating a clock signal at a corrected first frequency; a frequencyconverter, the frequency converter communicating with the frequencycorrection module to receive the clock signal at the corrected firstfrequency and outputting a clock signal at a second frequency to operatea positioning receiver portion of the hybrid communications device toreceive a wireless positioning signal.
 2. A system according to claim 1,wherein the communications portion comprises at least one of a cellulartelephone, a two-way pager and a network-enabled wireless communicationdevice.
 3. A system according to claim 1, wherein the clock sourcecomprises an oscillator.
 4. A system according to claim 3, wherein theclock source comprises a synthesizer.
 5. A system according to claim 1,wherein the frequency correction module comprises a temperaturefrequency control module.
 6. A system according to claim 5, wherein thetemperature frequency control module comprises a temperature frequencycontrol algorithm.
 7. A system according to claim 5, wherein thetemperature frequency control module comprises a temperature frequencycontrol circuit.
 8. A system according to claim 1, wherein the frequencycorrection module comprises an automatic frequency control module.
 9. Asystem according to claim 8, wherein the automatic frequency controlmodule comprises an automatic frequency control circuit.
 10. A systemaccording to claim 8, wherein the automatic frequency control modulecomprises an automatic frequency control algorithm.
 11. A systemaccording to claim 1, wherein the frequency correction module operateson manufacturing tolerance data.
 12. A system according to claim 1,wherein the frequency converter comprises a frequency divider.
 13. Asystem according to claim 1, wherein the positioning receiver portioncomprises a global positioning system receiver.
 14. A method forgenerating a frequency reference in a hybrid communications device,comprising: generating a clock signal at a first frequency in acommunications portion of the hybrid communications device; generating aclock signal at a corrected first frequency based on the clock signal atthe first frequency; generating a clock signal at a second frequencybased on the clock signal at the corrected first frequency to operate apositioning receiver portion of the hybrid communications device toreceive a wireless positioning signal.
 15. A method according to claim14, wherein the communications portion comprises at least one of acellular telephone, a two-way pager and a network-enabled wirelesscommunication device.
 16. A method according to claim 14, wherein thestep of generating a clock signal at a first frequency comprises a stepof exciting an oscillator.
 17. A method according to claim 16, whereinthe step of generating a clock signal at a first frequency comprisesoperating a synthesizer.
 18. A method according to claim 14, wherein thestep of generating a clock signal at a corrected first frequencycomprises a step of applying a temperature frequency control module. 19.A method according to claim 18, wherein the step of applying atemperature frequency control module comprises a step of executing atemperature frequency control algorithm.
 20. A method according to claim18, wherein the step of applying a temperature frequency control modulecomprises a step of operating a temperature frequency control circuit.21. A method according to claim 14, wherein the step of generating aclock signal at a corrected first frequency comprises operating anautomatic frequency control module.
 22. A method according to claim 21,wherein the step of operating an automatic frequency control modulecomprises a step of operating an automatic frequency control circuit.23. A method according to claim 21, wherein the step of operating anautomatic frequency control module comprises a step of executing anautomatic frequency control algorithm.
 24. A method according to claim14, wherein the step of generating a clock signal at a corrected firstfrequency comprises a step of operating on manufacturing tolerance data.25. A method according to claim 14, wherein the step of generating aclock signal at a second frequency comprises a step of operating afrequency divider.
 26. A method according to claim 14, wherein thepositioning receiver portion comprises a global positioning systemreceiver.
 27. A system for generating a frequency reference in a hybridcommunications device, comprising: a clock source in a communicationsportion of the hybrid communications device, the clock source generatinga clock signal at a first frequency; a frequency converter, thefrequency converter communicating with the clock source to receive theclock signal at the first frequency and outputting a clock signal at asecond frequency, the second frequency being used to operate apositioning receiver portion of the hybrid communications device toreceive a wireless positioning signal.
 28. A system according to claim27, wherein the communications portion comprises at least one of acellular telephone, a two-way pager and a network-enabled wirelesscommunication device.
 29. A system according to claim 27, wherein theclock source comprises an oscillator.
 30. A system according to claim29, wherein the clock source comprises a synthesizer.
 31. A systemaccording to claim 27, wherein the frequency converter comprises afrequency divider.
 32. A system according to claim 27, wherein thefrequency converter comprises a prescaler.
 33. A system according toclaim 27, wherein the positioning receiver portion comprises a globalpositioning system receiver.
 34. A method for generating a frequencyreference in a hybrid communications device, comprising: generating aclock signal at a first frequency in a communications portion of thehybrid communications device; generating a clock signal at a secondfrequency based on the clock signal at the first frequency to operate apositioning receiver portion of the hybrid communications device toreceive a wireless positioning signal.
 35. A method according to claim34, wherein the communications portion comprises at least one of acellular telephone, a two-way pager and a network-enabled wirelesscommunication device.
 36. A method according to claim 34, wherein thestep of generating a clock signal at a first frequency comprises a stepof exciting an oscillator.
 37. A method according to claim 36, whereinthe step of generating a clock signal at a first frequency comprises astep of operating a synthesizer.
 38. A method according to claim 34,wherein the step of generating a clock signal at a second frequencycomprises a step of dividing the clock signal at the first frequency.39. A method according to claim 38, wherein the step of generating aclock signal at a second frequency comprises a step of operating aprescaler.
 40. A method according to claim 34, wherein the positioningreceiver portion comprises a global positioning system receiver.